1. Field of the Invention
This invention provides a method and compositions for use in binding, detecting, and amplifying the detection of specific Target Nucleic Acid sequences in a sample with fidelity and accuracy, even in the presence of closely related but different nucleic acids. The binding involves the chaperoning and assembly of specific molecules into Target Binding Assemblies which specifically bind Target Binding Regions formed by the hybridization of Probe Nucleic Acids and Target Nucleic Acid sequences. The amplifying involves the chaperoning and assembly of specific molecules into Booster Binding Assemblies which specifically bind Booster Binding Regions formed by the hybridization of Booster Nucleic Acids with Probe Nucleic Acids, Target Nucleic Acids, or other Booster Nucleic Acids. A method, and compositions, involving Hairpin Nucleic Acids is also provided to enable control of the size of specifically or non-specifically elongated Booster Nucleic Acids and Booster Binding Assemblies used in the amplification. The detecting involves providing one or more detectable labels, including radioactive, light- or fluorescent-emitting, enzymatic, or other detectable or signal-generating molecules, in association with the Probe Nucleic Acid, the Target Binding Assembly, the Booster Nucleic Acid, the Booster Binding Assembly, or the Hairpin Nucleic Acid. Therapeutic and prophylactic uses of the Target Binding Assemblies and compositions for such use are also provided.
2. Background and Description of Related Art
There are an increasing number of cases in which it is important to be able to detect nucleic acids containing a specific sequence, hereinafter named Target Nucleic Acids (TNAs), in a sample. It is desirable to be able to detect the TNAs with the smallest number of processing steps, with the simplest components and to the exclusion of other similar but different nucleic acids, hereinafter named Cousin Nucleic Acids (CNAs). It is desirable to be able to detect specific TNAs to the exclusion of any and all CNAs in the detection sample without the necessity of amplification or other post-detection processing.
There are numerous methods which use immobilized or tagged nucleic acids as probes for TNAs. However, using known methods, it is difficult to discriminate between a TNA bound to the Probe Nucleic Acid (PNA) as opposed to a CNA bound to the PNA. For example, one or more base mismatches between the PNA and a CNA can still result in a CNA-PNA hybridization which is almost indistinguishable from a TNA-PNA hybridization. Thus, hybridization alone is not an optimal indicator that a PNA has hybridized to its unique and complementary TNA.
There are many situations in which a PNA would be used to try to determine whether a TNA was present in a sample which may contain CNAs. Hybridization of the PNA to any CNA in this situation would limit the diagnostic value that the PNA might have for the detection of a TNA, absent additional verification. Furthermore, it is desirable to be able to detect and localize TNAs with low copy numbers in samples which may contain many copies of CNAs, without the necessity of creating additional copies of the TNA. It would also be desirable to be able to confirm the presence of CNAs, independent of the TNAs, without the necessity of separating the CNAs and TNAs in the sample.
Furthermore, it would be desirable to be able to amplify the signal of even a low frequency hybridization of a particular TNA-PNA. For this purpose, a method of polymerizing multiple copies of a label, hereinafter referred to as a Booster Nucleic Acid (BNA) onto the TNA-PNA would be desirable.
The instant invention provides methods and compositions for achieving the foregoing desired objectives. As revealed by the following review, the instant compositions and methods have not been reported or suggested in the art. A general and comprehensive review of the state of art of nucleic acid detection is provided in Keller, H., M. M. Manak (1989) DNA Probes, Stockton Press.
A method has been reported for detecting base pair mismatches by chemical means in order to determine whether a PNA has hybridized to a CNA rather than to a TNA. In U.S. Pat. No. 4,794,075 to Ford et al., a method for distinguishing fragments of DNA which contain single base mismatches from their perfectly paired homologs is discussed. Single stranded regions within a duplex fragment are modified with carbodiimide, which reacts with unpaired guanine (G) and thymine (T) residues in DNA. Linear duplex DNA molecules do not react, while DNA molecules with single base mismatches react quantitatively. Following reaction with carbodiimide, the DNA molecules are fractionated on high percentage polyacrylamide gels such that modified and unmodified fragments can be distinguished. Ford et al. applied this technique in order to locate and purify DNA sequence differences responsible for phenotype variation and inherited disease. Although this method is useful for following variations in genetic material, it has a large number of steps, it requires costly components, and it does not offer a direct means of determining whether a PNA has hybridized to the TNA exclusive of CNAs in the sample.
There have been some attempts to assure that at least a portion of the hybridization between the PNA and another nucleic acid is complementary. One method involves the monitoring of transcription products which are produced if the PNA hybridizes to a nucleic acid sufficiently to be transcribed from a promoter site contained in the probe. U.S. Pat. No. 5,215,899 to Dattagupta discloses how specific nucleic acid sequences are amplified through the use of a hairpin probe which, upon hybridization with and ligation to a target sequence, is capable of being transcribed. The probe comprises a single stranded self-complementary sequence which, under hybridizing conditions, forms a hairpin structure having a functional promoter region, and further compromises a single stranded probe sequence extending from the 3' end of the hairpin sequence. Upon hybridization with a target sequence complementary to the probe sequence and ligation of the 3' end of the hybridized target sequence to the 5' end of the hairpin probe, the target sequence is rendered transcribable in the presence of a suitable RNA polymerase and appropriate ribonucleoside triphosphate (rNTPs). Amplification is accomplished by hybridizing the desired TNA sequence with the probe, ligating the TNA to the PNA, adding the RNA polymerase and the rNTPs to the separated hybrids, and allowing transcription to proceed until a desired amount of RNA transcription product has accumulated. That method generally and specifically involves the use of hairpin DNA formed with a single stranded unpaired end to anneal a target sequence. When the target sequence is bound, the production of RNA transcription products is enabled. Thus, the method involves the detection of secondary transcription products rather than the use of a nucleic acid binding assembly to directly immobilize and/or localize a target sequence. A CNA could easily bind to the probe, and the lack of complementarity would not necessarily interfere with the formation of a CNA-PNA hybrid which could then support the production of unwanted transcription products.
A CNA bound to the PNA might be detected if the lack of complementarity interferes with the susceptibility of the hybrid CNA-PNA pair to be cut by a restriction endonuclease. In U.S. Pat. No. 5,118,605 to Urdea and U.S. Pat. No. 4,775,619 to Urdea, novel methods for assaying a nucleic acid analyte were provided, which employ polynucleotides having oligonucleotide sequences substantially homologous to a sequence of interest in the analyte, where the presence or absence of hybridization at a predetermined stringency provides for the release of a label from a support. Various techniques are employed for binding a label to a support, whereupon cleavage of either a single or double strand, a label may be released from a support, and the release of the label can be detected as indicative of the presence of particular polynucleotide sequence in a sample. However, this technique has the shortcoming that a CNA-PNA pair could be cut by the restriction endonuclease, even if there is a mismatch, so long as the mismatch was outside of the endonuclease recognition region. This would lead to failure of the assay to identify a CNA-PNA hybrid.
Another method uses a branched DNA probe to detect nucleic acids. U.S. Pat. No. 5,124,246 to Urdea et al. discloses linear or branched oligonucleotide multimers useful as amplifiers in biochemical assays which comprise (1) at least one first single-stranded oligonucleotide unit (PNA) that is complementary to a single-stranded oligonucleotide sequence of interest (TNA), and (2) a multiplicity of second single-stranded, oligonucleotide units that are complementary to a single-stranded labeled oligonucleotide. Although amplified sandwich nucleic acid hybridizations and immunoassays using the multimers are described, the method has the limitation that PNA-CNA hybridization could occur and would result in production of unwanted signal.
In addition to methods for identification of TNAs, methods have been disclosed for the amplification of this DNA. In U.S. Pat. No. 5,200,314 to Urdea, an analyte polynucleotide strand having an analyte sequence (TNA) is detected within a sample containing polynucleotides by contacting the analyte polynucleotide with a capture probe (PNA) under hybridizing conditions, where the capture probe has a first binding partner specific for the TNA, and a second binding sequence specific for a solid phase third binding partner. The resulting duplex is then immobilized by specific binding between the binding partners, and non-bound polynucleotides are separated from the bound species. The analyte polynucleotide is optionally displaced from the solid phase, then amplified by PCR. The PCR primers each have a polynucleotide region capable of hybridizing to a region of the analyte polynucleotide, and at least one of the primers further has an additional binding partner capable of binding a solid-phase binding partner. The amplified product is then separated from the reaction mixture by specific binding between the binding partners, and the amplified product is detected. Although it is possible to confirm (by PCR) that a particular nucleic acid has hybridized the PNA, confirmation is expensive and involves multiple steps.
As for reports that involve the interaction of a double stranded nucleic acid and a DNA-binding protein, a method has been described whereby a sequence of immobilized DNA which contains binding sites for a single protein is used to purify that protein. U.S. Pat. No. 5,122,600 to Kawaguchi et al. discloses a DNA-immobilized microsphere comprising DNA chains having base sequences which specifically bind a particular protein, and a carrier having a particle size of not more than 50 .mu.m and not less than 0.01 .mu.m which does not adsorb any protein, said carrier and said DNA chains being bound to each other by a chemical bond, and a process for purifying a protein using said microsphere. As this is a purification method for a protein, it does not disclose a method of detection of a TNA nor a method whereby more than one protein is bound to a double stranded nucleic acid for the purposes of detection and localization of specific TNA sequences.
In EP 0 453 301, a method for detecting a polynucleotide target sequence in a sample was described, wherein sequences in a TNA are detected by hybridizing a first and a second PNA to the TNA Each of said first and second PNAs contained a pre-formed duplex sequence, or a duplex that is formed through chain extension, capable of binding a nucleotide sequence specific binding protein. A method for binding a nucleotide specific binding protein to a duplex formed between a TNA and a PNA only upon formation of a perfect duplex between the PNA and TNA is neither disclosed nor suggested.
In U.S. Pat. No. 4,556,643, a method was disclosed for the non-radioactive detection of specific nucleotide sequences in a sample which involved hybridization of a probe containing DNA binding protein specific sequences. However, this disclosure neither taught nor suggested a method for binding a nucleotide specific binding protein to a duplex formed between a TNA and a PNA only upon formation of a perfect duplex between sequences present in the PNA and sequences present in the TNA.